Lie on your back, contract lower abdominal muscles & then raise one leg, kept straight, hold for 10, lower. Repeat with other leg. 4 sets / leg.
Lie on your back, kness bent, contract lower abdominal muscles, lift hips from floor & hold for count of 10. X 4
Lie on front, lift leg 90 deg at knee & point at ceiling, raise leg off ground, hold 10. Switch legs, X 4
Twice a day. Every day. Don't stop. Especially when your backs better.
& what you've listed.
Press ups are great, build up to it. Start on your knees as suggested. 100 press up challenge is good way to motivate.
At least that's what's worked for me.
Losing 3 1/2 + stone has helped!!